Aluminum base alloy production



May 27, 1,969 P. ESSLINGER ETAL 3,445,920

ALUMINUM BASE ALLOY PRQDUCTION I Filed May 5. 1966 Sheet of s May 27, 1969 P. ESSLINGER ETAL 3,445,920

ALUMINUM BASE ALLOY PRODUCTION Sheet Filed May 5, 1966 f AVERAGE VALU Es LIMITING RANGE O J O 3 g 200 300 TEsT TEMPERATURE A: 5% Mn, 8% F2, BALANCE Al PREPARED ACCORDING TO lNVENTION B: 5. 5 0 in,

2.8 M ,0.5% Mn, 0.4% Cu, BALANCE Al CONVENTION/ALLY c: 6.0%Lu, 0.25%Mn, 0.1

PREPARED BALANCE A] May 27, 1969 P, ESSLINGER ETAL 3,445,920

ALUMINUM BASE ALLOY PRODUCTION Sheet Filed May 5. 1966 kplmm TEMPERING TEMPERATURE FIGB United States Patent O 3,445,920 ALUMINUM BASE ALLOY PRODUCTION Paul Esslinger, Stuttgart, Heinrich Winter, Eschborn Taunus, and Walter Wolf, Frankfurt am Main, Germany, assignors to the Federal Republic of Germany as represented by the Secretary of Defense, Bonn, Germany Filed May 5, 1966, Ser. No. 547,939 Claims priority, appliclgtigii 8(gfirmany, May 11, 1965,

Int. 'Cl. C21d 7/ i 4; B22d 19/00 US. Cl, 29472.3 4 Claims ABSTRACT OF THE DISCLOSURE An aluminum base alloy is produced by melting the alloy and passing it between closely spaced cooling and forming surfaces which compact the molten alloy into a thin sheet having a thickness of 1 mm. or less.

This invention relates to a method for producing ductile aluminum alloys of high strength at elevated temperatures.

It is known that the strength of metals at room temperature and elevated temperatures can be increased by suitable alloying additions. However, in malleable alloys,

the amount of such additives cannot, at present, be increased at will unless the alloying additive gives with the base metal an extensive area of mixed crystal formatio in the solid state.

When the amount of alloying additive exceeds the m axialloy because, in normal production, their size is in excess I of 1 m. Particles of such size are not able of hindering substantially the slippage inside the material in plastic deformation. Instead, they act mostly as nuclei for the 4 formation of internal cracks. v p I It is also known to prepare structures having finely distributed inclusions by applying high cooling rates. In order to obtain a reasonable increase of strength, the

inclusions must be very small and have an order of magv I nitude of 0.01 to 1pm.

In order to obtain dispersions of such fine particles, the cooling rate of the dispersions during casting must be extremely increased, to an order ,of magnitude of 10 to 10 C./sec. and higher. At such cooling rates, other known effects take place, such as precipitation'of metastable phases in line dispersions and extension of the area of mixed crystallization; both elfects can considerably increase the strength, particularly the high temperature strength.

Heretofore, it has not been possible to make use of this knowledge because the recited rapid cooling rates could be realized only at castings having a wall strength of less than 1 mm.

Such thin castings cannot be prepared with conventional casting procedures. In addition, cooling rates of such order of magnitude were difiicult to obtain because at beginning solidification the casting shrinks and an air gap is formed between the casting and mold, which interrupts the heat contact.

A sufficiently high cooling rate is obtained in the 3,445,920 Patented May 2 7, 1969 known atomization of melts. The thus obtained powder is then compacted; in this way, special aluminum alloys of good elevated temperature properties can be obtained. However, this method presents the following drawbacks:

The powder metallurgical processing is relatively complicated and increases the cost of the alloy. In addition, heat treatments are required at rather high temperatures, which in many alloys destroy the favorable structures. Thereby, oxide and oxide hydrate inclusions are unavoidable whose sizes, forms, and quantities cannot be controlled.

On heating, the oxide hydrates give off water which can react with the metallic components to form hydrogen. The oxide inclusions as well as the hydrogen reducethe ductility of the alloys.

Said drawbacks are avoided according to theinvention by melting an aluminum alloy, preferably without a crucible, by cooling the melt rapidly between at least two moving cooling bodies, and by forming the melt simul- ,taneously to thin bodies, e.g., films, of a thickness of about 1, preferably 0.1 to 0.5 mm. The thus obtained alloys having high ductility; and high strength at elevated temperatures; the alloying elements are segregated from stable ormetastable phases as finely dispersed particles by weight of chrome, Al-Cr-Si and Al-Mn-Si alloys containing up to 20% of thefalloying additives, and others.

According to a further embodiment of the invention, semifinished articles and workpieces of greaterthickness can be made from alloys by compacting a plurality of said thin shapes to packs by rolling or pressing, particularly at moderately elevated temperatures (press weld- 9 ing) to the desired end product. For'Al-Si alloys, for

instance, a suitable temperature is about 300 C. Such 'procedurejis possible because the thin shapes obtained by our method have a surprising workability which is far beyond the usual workability.

Our novel method offers the, possibility to prepare finished and semifinished articles, such as sheets, strips, 'and sections by deformation from alloys which heretofore in conventional casting methods were obtained so brittle as not to allow further working by technical deformation. This presents a considerable advance because the alloys prepared in accordance with the invention have a particularly advantageous fineistructure and at the sametime a surprisingly high strength, even at ele- 'vated temperatures. v p

When applying the method of the inevntion to heterogeneous alloys of conventional composition, their strength, workability and recrystallization temperature are considerably increased; this is of advantage particularly for the use of such alloys at elevated temperatures.

The invention will be described in more detail with reference to the accompanying drawings wherein:

FIG. 1 shows an apparatus suitable for carrying out the method of the invention;

FIG. 2 shows the variation of the tensile strength as a function of the temperature for alloys made in accordance with the invention in comparison to conventionally compared alloys, and

FIG. 3 is a diagram similar to FIG. 2', showing the variation of the tensile strength as a function of the tempering temperature.

Referring now first to FIG. 1, the reference numeral 1 represents a suitably wound induction coil in which the alloy 2 can be molten infree-floating condition. Any other siutable melting procedure can be employed, e.g., a so-called self-consuming electrode can be molten continuously by means of an electric are or electron beam. The molten alloy passes into the cooling device 3 which consists of at least two movable coolin-g bodies of high heat conductivity (e.g. copper or silver). In the example,

said cooling bodies have the form of movable plates which can be displaced rapidly against each other so as to form therebetween, with simultaneous uninterrupted cooling, the melt to thin bodies, e.g. films of at most 1 mm. thickness. Thereby, said plates act as molds following the shrinkage of the solidifying metal. A similar effect can be also accomplished, for example, by employing as cooling bodies rotating cylinders.

In the embodiment illustrated in the drawing, the cooling elements are actuated by the solenoids 4, which are switched on by the melt itself on its travel into the molds by means of the photoelectric cell 5. Said cell 5 is electrically connected to the solenoid 4 by means of a control device 6, which operates with a predetermined delay. By adjusting said delay with respect to the distance between photoelectric cell and cooling elements, we ensure that said cooling elements move quickly towards each other at the right moment.

The thickness of the films and e.g. also of wires can be adjusted by suitable control of the melting temperature, the rate of movement and pressure of the cooling elements and their distance, to the range of 0.1 to at most 1 mm.

The following examples are given to illustrate the invention.

Example 1 An aluminum base alloy having the composition 6% by weight manganese, 8% by weight iron, balance aluminum, was cast in conventional manner in a copper chill mold to round bars of 10 mm. diameter. On the other hand, the same alloy was used to prepare films of about 0.3 mm. thickness in accordance with the invention. While the conventionally cast rods were extremely brittle at elevated temperatures already at the slightest deformation, the films could be cold rolled by about 50% without any difiiculties. In the cold rolled state, they gave the values of cold and heat resistance shown in the hatched range A of FIG. 2. The curves B and C show the corresponding values of conventional aluminum alloys having comparable strength at low temperatures.

Example 2 Specimens were prepared from eutectic aluminum-silicon casting alloys, on the one hand, in conventional manner in sand or chill molds, and, on the other hand, as films by the process of the invention. The specimens were cold rolled and tested for their tensile strength at room temperature after tempering for 1 hour at the various temperatures indicated as abscissae in FIG. 3.

The dotted line shows the values measured on conventionally cast alloys. The fu l l e shows the tensile strength for specimens of the same alloy produced according to the invention.

The diagram shows that the method of the invention almost doubles the tensile strength and raises the recrystallization temperature by about C. In addition, the alloy made according to the invention had considerably better workability.

Example 3 Aluminum base alloys containing about 3% iron and 3% silicon, when cast by conventional methods, are workable only with difficulty. In contrast thereto, films or foils made by the method of the invention offer .a workability and deformability which are far superior to the properties attainable heretofore.

Example 4 For the manufacture of bolts having a diameter of 10 mm., as used for the production of heat resistant screws, discs of a diameter of 50 mm. were punched from a sheet of 0.3 mm. thickness of .an Al-Mn-Fe alloy obtained by the process of Example 1. 300 such discs were packed upon each other and compressed in an extrusion press at a pressure of 1500 atm. and at a temperature of 350 C. to the article. The high temperature tensile strength of the bolts was much higher than that of bolts made from the same alloy by conventional casting.

We claim:

1. A method of producing an aluminum base alloy having good ductility and high strength at elevated temperatures comprising passing a free-flowing melt of an aluminum base alloy through a narrow gap defined by cooling surfaces spaced from each other by not more than about 1 mm., solidifying the alloy in said gap, the sudden cooling in said gap precipitating the alloy elements in said alloy substantially as finely dispersed particles having .a diameter of 0.1 to 1 [.LIIL, and compressing the alloy, while being solidified, on its passage through said gap to a sheet of a thickness of at most 1 mm.

2. The method as claimed in claim 1 wherein the width of said gap at its narrowest point is 0.1 to 0.5 mm.

3. The method as claimed in claim 1 including the step of joining said sheets to articles of greater thickness.

4. The method as claimed in claim 3 superposing a plurality of said sheets and uniting the same at elevated temperatures.

References Cited UNITED STATES PATENTS 2,967,351 1/ 1961 Roberts et a1. 29-4205 3,147,521 9/1964 Boehm 29-528 X 3,214,805 11/1965 McKenica 164-75 X 3,368,273 2/ 1968 Maltsev et a]. 29-528 3,374,826 3/1968 Black 29-528 X JOHN F. CAMPBELL, Primary Examiner.

P. M. COHEN, Assistant Examiner.

US. Cl. X.R. 

